Recently, contact lens, particularly soft contact lens (hereinafter also referred to as SCL) have become very widely used for the purpose of vision correction or beauty. Wearing contact lens, however, places a load on eye though it varies between individuals.
The typical complaint from contact lens users is eye dryness. A healthy tear film is a structure of thin layers with about 7 μm thickness, which is composed of three layers: mucin, aqueous and lipid layers from the eyeball side and protects cornea from drying, stimulation by external environment or the like. In particular, the lipid layer in the nearest position to the external environment prevents evaporation of tear fluid, however, due to the cause such as thinning or destabilization of tear film, the lipid layer is also prone to become thin, inhomogeneous, or unstable, and evaporation of tear fluid is promoted, and thus dry eye symptom including eye desiccation is occurred. And such destruction (destabilization) of tear film causes spots wherein the lipid layer is extremely thin or not existed. These spots observed on the surface of tear film is called dry spots, and the time elapsed until the appearance of dry spots can be used for calculating the tear film breakup time (BUT), accordingly, the dry spots is thought to be one of the important indexes for diagnostic criteria of eye desiccation or dry eye (see Journal of the eye, 22 (3): 279-287, 2005). Thus, it is of great significance if the time until the appearance of dry spots can be delayed or the increase in number and area of dry spots under the same time between blinks can be suppressed, because these lead to the suppression of dry eye symptom including eye desiccation or eye strain.
It has also been known that even if a person has healthy eyes without lenses, when he wears contact lenses the tear film becomes inhomogeneous and he easily feels desiccation of the eyes, thus he is susceptible to dry eye. In particular, while wearing SCL, the tear film on the SCL has a tendency to become very thin and thus there is a phenomenon observed in which the lipid layer often becomes extremely thin on the SCL or the lipid layer is sometimes partially or totally absent. As a result, evaporation of tear fluid is increased, and evaporation of water from inside the SCL and eventually from under the SCL is promoted, which may cause eye dryness or corneal disorder (see Journal of the eye, 22 (3): 311-316, 2005).
Therefore, in order to ensure safety for the eyes of contact lens users, it is necessary to stabilize the tear film on the outside surface of the lens, particularly, lipid layer continuously and effectively.
A method of applying artificial tears was conventionally taken to treat eye dryness, however, the method of only using artificial tears could not achieve stabilization of tear film, and thus a sufficient effect could not be obtained. Therefore, a system for stabilizing the tear film surrounding the contact lens was proposed in which polyvinylpyrrolidone is adsorbed on the surface of anionic contact lens to increase water retention ability of the surface of the lens, and eye drops to the eye wearing a contact lens and a wetting solution used therefor were also proposed (JP 2001-247466 A). Furthermore, an ophthalmic liquid composition has been proposed in which long-chain alkyl derivatives of polysaccharides is used to promote and maintain the formation of trilaminar structure of tear film (JP 2007-77053 A). However, the systems and the compositions described in these documents have not sufficiently exerted an effect of stabilizing tear film, particularly lipid layer continuously and effectively.
Further, other problems associated with wearing contact lens include decreased contrast sensitivity. Contrast sensitivity is one of the criteria for evaluation of visual function, and it is a measure of the ability of distinguishing a slight difference of brightness. Decreased contrast sensitivity may lead, for example, to an accident because it is difficult for a person to distinguish the contrast between the road surface and obstacles while walking, or to an inconvenience in sports (especially, ball game) because it is difficult for a person to perceive the contrast between ball and background. It has been known that the decrease of contrast sensitivity is caused by an ophthalmic surgery such as keratorefractive surgery with the excimer laser, and aging, as well as wearing of contact lens. And there is a report that decrease of contrast sensitivity due to wearing of contact lens is associated with wearing of varifocal contact lens or soft contact lens for long term or use of extended-wear soft contact lens. As a solution to these problems, there is an attempt to change the contact lens itself, however, it has not been known that contrast sensitivity can be improved by an ophthalmic composition.
Meanwhile, ophthalmic solutions such as eye drops, eye washes or contact lens wetting solution have basically different purposes of use and they are handled independently in use. Thus, contact lens users are required to keep, for example, contact lens wetting solution and eye drops separately and use them independently. These solutions, however, are often similar in appearance because of the dosage and so on, despite of the difference in the purpose of use (application), therefore, there was a risk of misuse. For seller, there also was a risk of inducing misuses by consumers due to false recognition at providing information or mix-ups of products. Accordingly, there has been a wide demand from not only users but also sales persons for the development of products that can be used conveniently and safely with no risks of misuse.